At its inception radio telephony was designed, and used for, voice communications. As the consumer electronics industry continued to mature, and the capabilities of processors increased, more devices became available to use wireless transfer of data and more applications became available that operate based on such transferred data. Of particular note are the Internet and local area networks (LANs). These two innovations allowed multiple users and multiple devices to communicate and exchange data between different devices and device types. With the advent of these devices and capabilities, users, both business and residential, found the need to transmit data, as well as voice, from mobile locations.
The infrastructure and networks which support this voice and data transfer have likewise evolved. Limited data applications, such as text messaging, were introduced into the so-called “2G” systems, such as the Global System for Mobile (GSM) communications. Packet data over radio communication systems became more usable in GSM with the addition of the General Packet Radio Services (GPRS). 3G systems and, then, even higher bandwidth radio communications introduced by Universal Terrestrial Radio Access (UTRA) standards made applications like surfing the web more easily accessible to millions of users.
Even as new network designs are rolled out by network manufacturers, future systems which provide greater data throughput to end user devices are under discussion and development. For example, the so-called 3GPP Long Term Evolution (LTE) standardization project also known as Evolved UTRAN (E-UTRAN) standardization is intended to provide a technical basis for radio communications in the decades to come. Among other things of note with regard to LTE systems is that they will provide for downlink communications, i.e. the transmission direction from the network to the mobile terminal, using orthogonal frequency division multiplexing (OFDM) as a transmission format and will provide for uplink communications, i.e. the transmission direction from the mobile terminal to the network, using single carrier frequency division multiple access (SC-FDMA).
Cellular networks such as LTE systems are foreseen to cover diverse geographic regions. On the one hand they are anticipated to cover urban areas with a high density of buildings with indoor users, while on the other hand cellular networks should also provide access over large geographic regions in remote rural areas. In both scenarios it is challenging to cover the entire service area. Either huge parts are heavily shadowed from the Base Station (BS) or the link distances are very large so that radio propagation characteristics are challenging.
In order to cope with diverse radio propagation conditions, multi-hop communication has been proposed. By means of intermediate nodes, e.g., relays, the radio link is divided into two or more hops, each with better propagation conditions than the direct link. This enhances link quality which leads to increased cell edge throughput and coverage enhancements.
Relaying is considered for LTE-Advanced, also called 3GPP Release 10, as a tool to improve e.g. the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas. The relay node (RN) is wirelessly connected to the radio-access network via a donor cell controlled by a donor eNodeB (eNB). The RN transmits data to/from user equipments (UEs) controlled by the RN using the same air interface as an eNB, i.e. from a UE perspective there is no difference between cells controlled by a RN and an eNB.
In LTE data transmissions to/from a UE are under strict control of the scheduler located in the eNB or RN. Control signalling is sent from the scheduler to the UE to inform the UE about the scheduling decisions. This control signalling, comprising one or several Physical Downlink Control Channels (PDCCHs) as well as other control channels, is transmitted at the beginning of each subframe in LTE, using 1-3 OFDM symbols out of the 14 OFDM symbols available in a subframe for normal Cyclic Prefix (CP) and bandwidths larger than 1.8 MHz. For other configurations the numbers are slightly different. Downlink scheduling assignments, used to indicate to a UE that it should receive data from the eNB or RN, occur in the same subframe as the data itself. Uplink scheduling grants, used to inform the UE that it should transmit in the uplink, occur a couple of subframes prior to the actual uplink transmission.
Since the relay's transmitter causes interference to its own receiver, simultaneous eNB-to-RN and RN-to-UE transmissions on the same frequency resource may not be feasible unless sufficient isolation of the outgoing and incoming signals is provided e.g. by means of specific, well separated and well isolated antenna structures. Similarly, at the relay it may not be possible to receive UE transmissions simultaneously with the relay transmitting to the eNB. In particular, it may not be feasible for an intermediate node such as a relay to receive control information from a network node such as an eNB while transmitting control information in control signals to UEs controlled by the intermediate node.